{{Short description|Family of gastropods}} {{Automatic taxobox | fossil_range = {{fossil range|Cretaceous|Recent}} Cretaceous-Recent<ref name="Janssen 2007"/><!-- for Bellerophina --> | image = Atlanta01.jpg | image_caption = Drawing of ''Atlanta'' sp. | taxon = Atlantidae | authority = Rang, 1829 | type_genus = ''Atlanta'' | type_genus_authority = Lesueur, 1817 | subdivision_ranks = Genera | subdivision = See text }}
'''Atlantidae''' is a family of sea snails, holoplanktonic gastropod molluscs in the clade Littorinimorpha.
According to taxonomy of the Gastropoda by Bouchet & Rocroi (2005) the family Atlantidae has no subfamilies.
==Description== The Atlantidae is a group of holoplanktonic gastropods, which all demonstrate a strong adaptation to pelagic life, in the form of a lenticular, laterally flattened, aragonitic shell, the surface of which is further enlarged by the presence of a wide, and very thin and fragile, double-walled keel.<ref name="Janssen 2007"/> The apex is on the right side of the shell, the umbilicus on the left.<ref name="Janssen 2007"/> For the living animal the enlargement of the shell's surface serves 'to increase stabilization during swimming and sinking'.<ref name="Janssen 2007"/> This phenomenon results in the occurrence of superficially very similar adult shells in separate species, whereas the larval shells may be utterly different.<ref name="Janssen 2007"/>
Their body size is microscopic with a shell diameter of less than 1 cm. The foot has evolved into a muscular swimming fin. Their swimming fin extends anteriorly beneath their head. They swim with their ventral part upward through undulation of their swimming fin.
The shell is coiled dextrally (i.e. clockwise). The thin, double-walled keel of the shell extends outward from the last shell whorl. The apex of the shell is found on the right side, the umbilicus on the left side. The shell and keel can be calcareous (genus ''Atlanta''), or composed exclusively of conchiolin (genus Oxygyrus), or the shell can be calcareous and its keel composed of conchiolin (genus ''Protatlanta''). The snails of this family can retract into their shell and close it off with a cartilaginous, flexible operculum.
==Genera== Genera in the family Atlantidae include:
* ''Atlanta'' Lesueur, 1817 - type genus * ''Oxygyrus'' Benson, 1835 - monospecific, it has only one species ''Oxygyrus keraudrenii'' (Lesueur, 1817) * ''Protatlanta'' Tesch, 1908 - monospecific in extant species;<ref name="Janssen 2007"/> a few fossil species have been described * † ''Bellerophina'' d'Orbigny, 1843 * † ''Eoatlanta'' Cossmann, 1888 * † ''Mioatlanta'' di Geronimo, 1974
Recent Atlantidae, in the present concept, comprise three genera, two of which, ''Oxygyrus'' Benson, 1835, and ''Protatlanta'' Tesch, 1908, are considered monospecific.<ref name="Janssen 2007"/> In ''Protatlanta'', however, a few additional fossil species have been described.<ref name="Janssen 2007"/> Both genera are characterised by partially uncalcified (conchiolin) shell portions.<ref name="Janssen 2007"/> Additional fossil genera considered to belong in the Atlantidae are ''Bellerophina'' d'Orbigny, 1843 (Cretaceous), ''Eoatlanta'' Cossmann, 1888 (Paleocene-Eocene) and ''Mioatlanta'' di Geronimo, 1974 (Miocene).<ref name="Janssen 2007"/> Only few ''Atlanta'' species are known from the fossil record, the oldest one being ''Atlanta arenularia'' Gougerot & Braillon, 1965 is from the Bartonian of the Paris Basin, which differs considerably from typical ''Atlanta'' by its cornucopia shape.<ref name="Janssen 2007"/>
==Ecology== Atlantids are negatively buoyant. During the day, they have to swim to maintain their position. At night they secrete strands of buoyant mucus to which they attach themselves. They are active predator locating their prey visually.
==References== This article incorporates CC BY-3.0 text from the reference <ref name="Janssen 2007">{{cite journal| author=Janssen A. W.| title=Holoplanktonic Mollusca (Gastropoda: Pterotracheoidea, Janthinoidea, Thecosomata and Gymnosomata) from the Pliocene of Pangasinan (Luzon, Philippines)| journal=Scripta Geologica| year=2007| volume=135| url=http://www.scriptageologica.nl/07/nr135/a02| access-date=2010-08-19| archive-url=https://web.archive.org/web/20110724165136/http://www.scriptageologica.nl/07/nr135/a02| archive-date=2011-07-24| url-status=dead}}</ref> {{Reflist}}
==External links== {{Commons category|Atlantidae}} * [http://tolweb.org/Atlantidae/28732 Seapy, Roger R. 2008. Atlantidae Rang, 1829. Version 29 December 2008 (under construction); Tree of Life Web Project : Atlantidae]
{{Taxonbar|from=Q756491}} {{Authority control}}
Category:Atlantidae Category:Littorinimorpha Category:Gastropod families